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Answers to experimental questions are developed according to results from
experimental protocols. The challenge is to address a question so that the answer is valid. Analysis of these results must, therefore, take into account the experimental
conditions under which they were obtained. Moreover, an interpretation of results is always limited to the confines of the experimental conditions. There are several
approaches to experimental design to try to realize the most valid answers.
The simplest designs to execute are acute experiments in which all
variables are controlled except for the variable under examination. In experiments with animals this usually means that anesthesia is used. If the experimental question
involves the cardiovascular system, then the effects of anesthesia on cardiovascular parameters have to be taken into account.
Truly long-term, chronic experiments to study the cardiovascular system
can be designed to examine the variables in question in intact conscious animals. These experiments can be elegant but there are many new variables which must now be
controlled such as light/dark cycles, environmental stimuli such as temperature and noise, olfactory stimuli and potential long-term stressors such as cage bedding, social
interactions and other behavioral factors. One can also quickly appreciate that in a design in which repetitive measures are made in each animal over time that loss of a
data point in a specific animal can effectively remove that animal from the study, at a great expense in lost time.
Acute experiments in chronically instrumented mice: These experiments take
advantage of short-term observations but avoid anesthetics and acute surgical stress.
Several Approaches
1. Acute Experiments
- simplest to execute but often the most difficult to design
- In the perfect design all variables are controlled except for the
variable being examined
- In acute animal experiments, the design usually calls for the use of
anesthesia which often leads to components of the experiment which are difficult to explain, because anesthesia can have powerful effects on the cardiovascular system.
- ether, pentobarbital sodium, clorose urethane affect mean
arterial pressure, cardiac output, heart rate and total peripheral resistance
- anesthesia also has strain dependent effect, producing differing
cardiovascular effects on different strains with different anesthetics
- Therefore, the challenge is to design an acute experiment so that
anesthesia is less important
2. Chronic Experiments: an alternative to acute experiments
instrument————- 5-7 days recovery————-follow over time
- 24 hour hemodynamic considerations such as diurnal variation which
must be taken into account by monitoring lights and other environmental stimuli
- primary consideration: how many days the experiment should last;
although one can think of many elegant experiments, they can end up being costly if there is failure on day 5 or after
- Perhaps the most practical type of experiment is one which performs
acute observations on chronically instrumented animals. Chronic studies in mice necessitate the availability of instruments appropriately small scaled for implant.
Aseptic Surgery
- Follow recommended guidelines & common sense
Healthier animals yield better science
- Sterility: follow aseptic techniques; all instruments and gloves,
mask, drapes, implants, sutures should be sterile
- Use top quality surgical instruments: Buying the instruments
constitutes an initial investment, but the instruments will last for a long time if properly maintained
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